The present invention relates to an interconnection structure of electric conductive wiring.
The present application claims priority from Japanese Patent Application Laid-Open No. 2002-353496, the disclosure of which is incorporated herein by reference.
As means for interconnecting respective conductive wiring of a pair of objects to be interconnected (hereinafter referred to as interconnection objects) physically and electrically, there is known an interconnection technology using a thermocompression bonding of interconnection portions of the conductive wiring sandwiching an anisotropic conductive film (ACF) between the respective interconnection portions. The anisotropic conductive film is an adhesive film made of adhesive such as thermoplastic resin or theromosetting resin containing conductive particles such as metallic particles or metallic coating plastic particles, anisotropic conductivity of which is assigned by scattering the conductive particles into the adhesive. The film enables an electric interconnection of a fine wiring pattern only through a thermocompression bonding process. Consequently, the film has been widely available in an interconnection of panel electrodes of a flat-panel such as LCD or organic EL and a Flexible Printed Circuit (FPC), or a Tape Automated Bonding (TAB) tape or the like (see, for example, Japanese Patent Application Laid-Open No. 2002-258767, or Japanese Patent Application Laid-Open No. Japanese Patent Application Laid-Open No. Hei.11-212496).
FIGS. 1A and 1B are explanatory views illustrating a conventional interconnection structure of the conductive wiring using such an anisotropic conductive film. In more detail, FIG. 1A is a cross-sectional view sectioned by a plane perpendicular to the conductive wiring, and FIG. 1B is a cross-sectional view sectioned along an I-I line shown in the FIG. 1A. The interconnection structure is formed through a thermocompression bonding between a conductive wiring 122 formed on a surface of a supporting body 121 as one interconnection object and a conductive wiring 132 formed on a surface of a supporting body 131 as the other interconnection object, sandwiching an anisotropic conductive film 140, which contains conductive particles 142, between these two conductive wirings. The conductive wirings 122 and 132 are electrically connected with each other through conductive particles 142 after the compression bonding is achieved. Because the conductive particles 142 are scattered in an insulating adhesive at the non-existing regions 146 of the conductive wirings (gaps between the conductive wiring patterns), an insulating state thereof is held between adjacent conductive wirings. Hence, through only the thermocompression bonding, it is possible for the conductive wirings 122 and 132 to be connected electrically with each other according to the respective wiring patterns as well as an adhesion of the interconnection objects.
In the conventional interconnection structure of conductive wiring using the anisotropic conductive film as shown in FIG. 1B, the adhesive, which serves as a base material of the anisotropic conductive film 140, becomes fluid at the time of the thermocompression bonding. As a result, there occurs a phenomenon that a part of the conductive particles 142 maintained in the adhesive between conductive wirings 122 and 132 is pushed out into each gap 146 between adjacent conductive wirings.
Because the conductive wirings of electronic apparatus have been recently desired to be more high-density, wiring patterns with narrow pitches are adopted in their interconnection structures of conductive wiring. Hence, the density of the conductive particles 142 becomes over-dense in the narrow gap 146, when the fluidization of the adhesive is blocked locally.
As shown in FIG. 1B, for instance, when an insulating layer 133 covers a surface on which the conductive wiring of an interconnection object is formed, there may occur a phenomenon that an edge of the insulating layer 133 facing on the interconnection portion blocks a flow of the adhesive in anisotropic conductive film 140. Thereby, the conductive particles 142 may stay over-densely in the gap 146 near the edge of the insulating layer 133. This may cause a shortage between adjacent conductive wirings, so called “shortage in wiring pattern”.
As further shown in FIG. 1B, suppose that an interconnection object having a supporting body 131 a surface of which is covered with the insulating layer 133 except for the surface of the interconnection portion, is interconnected with the other interconnection object at the end of the supporting body 121. When the supporting body 131 is bent, a maximum bending moment is applied on the supporting body 131 at a location of the end of the insulating layer 133, and causes a stress concentration at the end of the insulating layer 133. This causes the other problem that a destruction of the interconnection object may occur at the portion of the stress concentration, if an excess bending is applied thereon.
On the contrary, when the insulating layer 133 of the supporting body 131 is overlapped on the other supporting body 121 to be interconnected with each other, a flow of the adhesive in the anisotropic conductive film 140 is blocked completely at the end of the insulating layer 133. Thus, the problem of the shortage in the wiring patterns more often occurs than one as described previously.